The present invention is directed to a navigation system for an Automatic Guided Vehicle (AGV). In particular, the invention is directed to a laser based navigation system which is capable of guiding the AGV when the AGV's conventional navigation laser is blocked by stacked product or the like.
Typical laser guided AGV's use a navigation laser mounted on top of the vehicle which rotates along a horizontal plane as the AGV travels throughout the facility and senses reflective wall targets mounted at intervals on the walls and columns. Once two or more targets are located, the AGV is able to identify and update its current location using a triangulation algorithm in the control software. This control software also directs additional calculations to plot the AGV's course on its way to the next pick or drop location. The AGV may also use a secondary navigational system known as dead reckoning. Dead Reckoning tracks the rotation and angle of the drive wheel to provide location information which is used to confirm the vehicle's position, thereby increasing navigation accuracy.
In some applications, such as warehouse storage and retrieval, product is stacked in lanes or rows which are higher than the navigation laser. When the AGV is required to pick or drop product in a lane, the stacked product in adjacent lanes may block the line of site from the navigation laser to the reflective targets. Once the reflective targets are blocked, the AGV is not able to determine its location and thus cannot navigate.
Several alternatives to the laser based navigation system may be used in facilities which contain rows of high stacked product. However, these systems are not without their problems.
For example, the magnetic guidance navigation system uses a Hall effect sensor mounted on the AGV to detect magnets mounted in the floor of the facility along the intended path of the vehicle. In this type of system, the AGV typically uses dead reckoning to guide the vehicle from magnet to magnet. As the AGV drives over a magnet, the Hall effect sensor will pinpoint the vehicle's location, and that information is used to correct the position of the vehicle. However, this system requires that a large number of magnets be buried in the floor along the intended path of the vehicle. Consequently, the magnetic guidance system does not allow the vehicle's path to be changed easily should the need arise. In addition, this system requires a substantial investment in materials and labor for installing the magnets.
In a wire guidance navigation system,the AGV employs an antenna to detect a specific signal radiated by a wire embedded in the floor of the facility along the intended path of the vehicle. As the AGV drives over the wire, the antenna pinpoints its location and that information is used to correct the heading and position of the vehicle. However, this system requires that a large amount of cable be buried in the floor along the intended path of the vehicle. Thus, as with the magnetic guidance navigation system, the wire guided system does not allow the vehicle's path to be changed easily and requires a substantial investment in materials and labor for installing the cables.
In a gyroscopic navigation system, a gyroscopic sensor is used to provide accurate heading information for the AGV. Similar to the magnetic guidance navigation system, an AGV equipped with a gyroscopic navigation system will use dead reckoning to track its location. The AGV will then use the information from the gyroscope to correct its heading. In this type of system, the distance the vehicle traveled must be measured by odometry of the drive wheel. However, the gyroscopic sensor is expensive. In addition, the sensor is prone to drift. Therefore, the sensor requires periodic calibration and maintenance to ensure its accuracy.
In a natural feature navigation system, the AGV uses a laser to scan the area of the facility around the vehicle. The information obtained by the laser is then compared to a specially generated map of the facility to determine the location of the vehicle. However, the map usually must include a large number of static and unique structures such as walls, doorways, columns, etc. to allow the area being scanned to be properly located in the map. Consequently, this system is usually not suitable for use in warehouses, which typically are very open and have few static structures.
In a ceiling guidance navigation system, the AGV uses a camera to identify unique markers positioned on the ceiling of the facility. The AGV then determines its location by triangulating from multiple markers. However, the markers may become obstructed by stacked product. Therefore, this system suffers from the same problems as the traditional laser based navigation system.